Fixing device and image forming apparatus

Abstract

Disclosed is a fixing device including: an endless belt member that is rotatably provided; a pressure member that abuts on the belt member to form a nip; and a heating member that is provided in contact with or not in contact with the belt member and is configured to heat the belt member; wherein when a length of the belt member that faces the heating member in a contact or non-contact manner in a rotation direction of the belt member is defined as a heating length Lh, and a length of the belt member that abuts on the pressure member in the rotation direction of the belt member is defined as a nip length Ln, the heating length Lh is set with respect to the nip length Ln to satisfy a relationship, −2.5*Ln+75≤Lh≤95 and 16≤Ln≤27.

What is claimed is: 
     
         1 . A fixing device comprising:
 an endless belt member that is stretched by a plurality of stretching members and is rotatably provided;   a pressure member that is provided to face the belt member, abuts on the belt member to form a nip, and is configured to cooperate with the belt member to nip and convey a recording material at the nip; and   a heating member that is provided in contact with or not in contact with the belt member and is configured to heat the belt member;   wherein when a length of the belt member that faces the heating member in a contact or non-contact manner in a rotation direction of the belt member is defined as a heating length Lh, and a length of the belt member that abuts on the pressure member in the rotation direction of the belt member is defined as a nip length Ln,   the heating length Lh is set with respect to the nip length Ln to satisfy a relationship,   
       
         
           
             
               
                 
                   
                     - 
                     2.5 
                   
                   * 
                   Ln 
                 
                 + 
                 75 
               
               ≤ 
               Lh 
               ≤ 
               
                 95 
                 ⁢ 
                     
                 and 
                 ⁢ 
                     
                 16 
               
               ≤ 
               Ln 
               ≤ 
               27. 
             
           
         
       
     
     
         2 . The fixing device according to  claim 1 ,
 wherein an abutting pressure between the belt member and the pressure member is 0.05 [MPa] or more.   
     
     
         3 . The fixing device according to  claim 1 ,
 wherein the plurality of stretching members includes a supporting member configured to support the belt member in contact with the belt member at a position facing the pressure member via the belt member.   
     
     
         4 . The fixing device according to  claim 3 ,
 wherein the plurality of stretching members includes a stretching member that is provided in contact with the belt member at a position different from the supporting member and is configured to stretch the belt member,   the heating member also serves as the stretching member, and   a length of the belt member that is in contact with the heating member in the rotation direction of the belt member is defined as the heating length Lh.   
     
     
         5 . The fixing device according to  claim 3 ,
 wherein the plurality of stretching members includes a stretching member that is provided in contact with the belt member at a position different from the supporting member and is configured to stretch the belt member,   the heating member is provided not in contact with the belt member at a position facing the stretching member via the belt member, and   a length of the belt member that faces the heating member in a non-contact manner in the rotation direction of the belt member is defined as the heating length Lh.   
     
     
         6 . The fixing device according to  claim 3 ,
 wherein the plurality of stretching members includes a first stretching member that is provided in contact with the belt member at a position different from the supporting member and is configured to stretch the belt member, and a second stretching member that is provided in contact with the belt member at a position between the first stretching member and the supporting member and is configured to stretch the belt member   the heating member includes a first heating member that also serves as the first stretching member, and a second heating member that also serves as the second stretching member, and   a length of the belt member that is in contact with the first heating member and the second heating member in the rotation direction of the belt member is defined as the heating length Lh.   
     
     
         7 . The fixing device according to  claim 6 ,
 wherein the first heating member and the second heating member are in contact with an inner peripheral surface of the belt member.   
     
     
         8 . The fixing device according to  claim 6 ,
 wherein one of the first heating member and the second heating member is in contact with an inner peripheral surface of the belt member and another is in contact with an outer peripheral surface of the belt member.   
     
     
         9 . The fixing device according to  claim 3 ,
 wherein the supporting member also serves as the heating member.   
     
     
         10 . The fixing device according to  claim 1 , further comprising:
 a temperature detection member configured to detect a temperature of the heating member or the belt member,   wherein the nip length Ln and the heating length Lh are set to satisfy the relationship while the temperature is in a range up to a maximum temperature of a guaranteed operating temperature of the temperature detection member.   
     
     
         11 . An image forming apparatus comprising: an image forming portion configured to form an image on a recording material; and the fixing device according to  claim 1 . 
     
     
         12 . The image forming apparatus according to  claim 11 ,
 wherein an abutting pressure between the belt member and the pressure member is 0.05 [MPa] or more.   
     
     
         13 . The image forming apparatus according to  claim 11 ,
 wherein the plurality of stretching members includes a supporting member configured to support the belt member in contact with the belt member at a position facing the pressure member via the belt member.   
     
     
         14 . The image forming apparatus according to  claim 13 ,
 wherein the plurality of stretching members includes a stretching member that is provided in contact with the belt member at a position different from the supporting member and is configured to stretch the belt member,   the heating member also serves as the stretching member, and   a length of the belt member that is in contact with the heating member in the rotation direction of the belt member is defined as the heating length Lh.   
     
     
         15 . The image forming apparatus according to  claim 13 ,
 wherein the plurality of stretching members includes a stretching member that is provided in contact with the belt member at a position different from the supporting member and is configured to stretch the belt member,   the heating member is provided not in contact with the belt member at a position facing the stretching member via the belt member, and   a length of the belt member that faces the heating member in a non-contact manner in the rotation direction of the belt member is defined as the heating length Lh.   
     
     
         16 . The image forming apparatus according to  claim 13 ,
 wherein the plurality of stretching members includes a first stretching member that is provided in contact with the belt member at a position different from the supporting member and is configured to stretch the belt member, and a second stretching member that is provided in contact with the belt member at a position between the first stretching member and the supporting member and is configured to stretch the belt member   the heating member includes a first heating member that also serves as the first stretching member, and a second heating member that also serves as the second stretching member, and   a length of the belt member that is in contact with the first heating member and the second heating member in the rotation direction of the belt member is defined as the heating length Lh.   
     
     
         17 . The image forming apparatus according to  claim 16 ,
 wherein the first heating member and the second heating member are in contact with an inner peripheral surface of the belt member.   
     
     
         18 . The image forming apparatus according to  claim 16 ,
 wherein one of the first heating member and the second heating member is in contact with an inner peripheral surface of the belt member and another is in contact with an outer peripheral surface of the belt member.   
     
     
         19 . The image forming apparatus according to  claim 13 ,
 wherein the supporting member also serves as the heating member.   
     
     
         20 . The image forming apparatus according to  claim 11 , further comprising:
 a temperature detection member configured to detect a temperature of the heating member or the belt member,   wherein the nip length Ln and the heating length Lh are set to satisfy the relationship while the temperature is in a range up to a maximum temperature of a guaranteed operating temperature of the temperature detection member.